This invention relates to industrial controllers and more particularly to evaluating the performance of industrial controllers.
Industrial process controllers (hereinafter, simply “controllers”) have many different configurations and are used in many different applications. Controllers may be mounted in a control room or may be part of a distributed control system. Controllers are designed to maintain a process variable at a desired reference point known as a set point. Process variables can be flow, pressure, temperature, consistency, speed, current, level, pH, etc. A conventional example of how a controller may be physically connected in an industrial process is shown in the functional block diagram of FIG. 1. In this example, a controller has an output that is converted into pressure to move a final control element, which in this example is a control valve. Movement of the control valve causes a change in the flow of material through a pipe. An instrument (such as transmitter with a sensor) measures a simple differential pressure in the pipe and transmits a current signal representative of the measurement back to the controller. This arrangement is a control loop in one of its simplest forms.
A control loop, such as the one described above can experience a problem that results in poor control of the process variable. The problem can be with the final control element, the sensor, tuning parameters of the controller, or something else. If the control loop is isolated or is only one of a handful of control loops, an experienced control engineer can usually analyze the control loop and determine what the problem is within a reasonable period of time. In a large industrial facility, however, it is not uncommon to have hundreds of control loops with hundreds of controllers. In such an industrial facility, it is difficult, to say the least, to determine which control loops are experiencing problems, especially when a problem in one control loop may adversely affect other control loops.
Based on the foregoing, there is a need in the art for a method for helping a control engineer to monitor a plurality of control loops and to identify and diagnose any of those control loops that are experiencing problems. The present invention is directed toward such a method.